740, in its earlier incarnation as CBL, used to be a regular when I was a kid in Medford. Plus CBM (Montreal 940), CKAC (Montreal 730), CKGM (Montreal 980 and 990), CKLM (1570 Laval/Montreal), CJMS (1280 Montreal). Plus CHUM (Toronto 1050) and CFRB (Toronto 1010). Plus CBA (Moncton NB 1070), CHML (Hamilton ON 900) and last but not least, The Big 8, CKLW (Windsor ON 800). If I was in the car, near the NH state line, then I could also pick up CKVL (850 Verdun/Montreal) battling with WHDH, and CBF (690 Montreal, usually drowned out by WRKO).
The CBC stations (CBL, CBM, CBA) have all moved to FM, as have many other Canadian AM stations. Some of the AM stations that moved have been replaced, but no one seems to want most of the frequencies that were abandoned. It's weird, because USA stations cannot improve their signals if they are on one of the vacant Canadian frequencies even though they have not been used for many years. WMEX before the recent changes, had to protect CJRS in Sherbrooke QC even though they have been off the air since 1994 with no takers for the frequency.